Abstract

Premise of research. Despite some recent progress on the systematics of the Leguminosae, the relationship between some genera as well as their circumscriptions remain uncertain. Here we investigate the relationships between Stryphnodendron and closely related genera in the Piptadenia group, a clade of problematic taxonomy and for which a robust phylogenetic hypothesis is still lacking.
Methodology. Taxonomic sampling included 23 species of Stryphnodendron (77% of the genus), and representatives of genera of the Piptadenia group. DNA (matK/trnK, trnD-trnT, trnL-trnF, ITS) sequences comprising a dataset with 6798 bp and 95 terminals were used in parsimony and Bayesian analyses. A set of 16 morphological characters were mapped on the estimated phylogeny to evaluate clade synapomorphies and character evolution.
Pivotal results. Our increased molecular and taxonomic sampling improved the resolution of a previously largely unresolved clade that included Microlobious, Parapiptadenia, Pityrocarpa, Pseudopiptadenia, and Stryphnodendron. Major lineages within this clade are: an early diverging clade containing the sister genera Parapiptadenia and Pseudopiptadenia; the genus Pityrocarpa with Pseudopiptadenia brenanii nested within it; and a Stryphnodendron including the monotypic genus Microlobius. Samples of Stryphnodendron grouped into three strongly-supported clades: a group of seven species bearing large leaflets and fewer pairs of pinnae, sister to Microlobius foetidus; a clade containing samples of S. duckeanum; a large and poorly-resolved clade containing the remaining species of Stryphnodendron, including species with small leaflets and higher number of pinnae, and highly specialized dwarf subshrubs adapted to savanna fire regimes. Lack of resolution within this clade suggests rapid and recent diversification in both savannas and rainforests in the neotropics.
Conclusions. Our findings highlight the importance of densely sampled phylogenies to rigorously test the monophyly of genera. Key morphological characters are proposed to assist generic delimitations in the Piptadenia group. New taxonomic rearrangements are needed in order to accommodate the results presented here.